Hot Water Recirculation Control Unit and Method

ABSTRACT

A hot water recirculation control unit has a housing, a male wall plug integrated into a first wall of the housing, an electrically-operable power switch, female wall plug integrated into a second wall of the housing, control circuitry including a processor, having an output enabled to switch the electrically-operable power switch, and signal ports enabled to receive signals from two temperature sensors and at least one flow sensor. The control circuitry switches the electrically-operable power switch on or off, providing power to or disconnecting power from the standard female electrical wall plug, based on presence and value of signals received at the one or more input signal ports.

CROSS-REFERENCE TO RELATED DOCUMENTS

The present invention claims priority to a U.S. provisional patent application 62/110,360, filed on Jan. 30, 2015 and entitled “Control system for using existing plumbing to signal a hot water recirculation pump to turn on”, disclosure of which is incorporated herein at least by reference,

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is in the field of hot water management and distribution and pertains more particularly to methods and apparatus for maintaining expedient hot water availability in a plumbing architecture.

2. Discussion of the State of the Art

In the field of hot water management and distribution, hot water heaters are often deployed in commercial or residential plumbing systems. In a typical installation a hot water heater has an incoming line (cold water) and an outgoing line (hot water). Water may be heated by burning propane or natural gas or by electrical means to attain a temperature suitable for the residence or commercial application.

One problem with typical water heater operation is when a draw occurs in the hot water plumbing after perhaps a long delay and the water in the pipes has cooled. Hence a period of wait time is needed after initial draw before the user actually has hot water available at the draw point in the plumbing. This causes water (cold draw) to be wasted until hot water from the water heater reaches the draw point. In an attempt to solve this problem, houses have been designed to have a hot water plumbing loop which passes near to all plumbing fixtures that use hot water. Water recirculation pumps were designed into the system to continually circulate hot water through the hot water plumbing loop and water heater. More particularly, the water flow may be constant through the hot water heater while the pump is running, thus ensuring that hot water is immediately available at any draw point in the building.

One problem with a hot water system using a recirculation pump that is always on is the energy that is wasted (gas and/or electricity) as heat is lost through the piping and for running the pump. But if the pump is turned off the pipes will cool until the pump is powered back on. In some installations timers are added to regulate the amount of time the pump is running in an attempt to conserve energy. However strict schedule requirements arise for the beneficiaries of the hot water such as using hot water only during a scheduled time window. And the energy saved by using a timer is negatively correlated with the convenience of having hot water. Another alternative is to install switches to power on the recirculation pump on demand. A problem here is that this requires wiring to all the desired draw-point fixtures. Therefore, what is clearly needed is a control system for managing hot water distribution in a plumbed system that eliminates or reduces the above problems.

BRIEF SUMMARY OF THE INVENTION

In one embodiment of the invention a hot water recirculation control unit is provided, comprising a housing, a standard male electrical wall plug integrated into a first wall of the housing, the male wall plug connected to hot, neutral and ground electrical conductors in electrical circuitry within the housing, an electrically-operable power switch in the circuitry of the controller, connected on an input side to the hot electrical conductor, a standard female electrical wall plug integrated into a second wall of the housing, connected to neutral and ground and to the output terminal of the electrically-operable power switch, control circuitry including a processor, connected to the electrical conductors, the control circuitry having an output enabled to switch the electrically-operable power switch, and one or more input signal ports enabled to receive signals from two temperature sensors and at least one flow sensor, the signal ports connected to the control circuitry. The control circuitry switches the electrically-operable power switch on or off, providing power to or disconnecting power from the standard female electrical wall plug, based on presence and value of signals received at the one or more input signal ports.

In one embodiment the control circuitry switches the electrically-operable power switch on, providing power to the standard female electrical wall plug, in response to a signal that the flow sensor senses positive flow, and a pre-set difference in temperature is sensed between the two temperature sensors. Also in one embodiment the unit further comprises a mechanism enabling adjustment of the preset difference in temperature . Also in one embodiment the unit further comprises a manual input enabled to switch the electrically-operable power switch on and off. And in one embodiment the control circuitry comprises one or more timing mechanisms for improving reliability of operation.

In another aspect of the invention a hot water recirculation system is provided, comprising a water heating source, a pipe loop from the water heating source supplying heated water to a plurality of draw points and returning to an input of the hot water heating source, a cold water supply line to the hot water heating source, a water pump in the pipe loop after the draw points and before the input to the water heating source, a flow sensor in the pipe loop to indicate positive flow of water, indicating a draw at one of the plurality of draw points, a first temperature sensor coupled to the pipe loop near the outlet of the water heating source, a second temperature sensor coupled to the pipe loop at a point after the plurality of draw points, and a controller having an electrical power input from a power source, an electrical power output to the water pump, and control circuitry enabled to switch power from the power source to the output to the water pump. Signals from the flow sensor and the first and second temperature sensors are coupled to the control circuitry and the control circuitry switches power from the power source to the power output to the water pump, based on presence and value of signals received from the flow sensor and the temperature sensors.

In one embodiment the control circuitry switches power to the water pump in response to a signal that the flow sensor senses positive flow, and a pre-set difference in temperature sensed between the two temperature sensors. Also in one embodiment the system further comprises a mechanism coupled to the control circuitry enabling adjustment of the preset difference in temperature. Also in one embodiment the system further comprises a manual input to the control circuitry enabled to switch power to the water pump, overriding the control circuitry. And in one embodiment the control circuitry comprises one or more timing mechanisms for improving reliability of operation.

In yet another aspect of the invention a hot water recirculation method is provided, comprising providing a pipe loop from a water heating source to a plurality of draw points and returning to an input of the hot water heating source, providing a cold water supply line to the water heating source, providing a water pump in the pipe loop after the draw points and before the input to the water heating source, sensing flow by a flow sensor in the pipe loop to indicate positive flow of water, indicating a draw at one of the plurality of draw points, sensing a first temperature by a first temperature sensor coupled to the pipe loop near the outlet of the water heating source, sensing a second temperature by a second temperature sensor coupled to the pipe loop at a point after the plurality of draw points, monitoring flow indication from the flow sensor and temperatures sensed by the temperature sensors at a controller having an electrical power input from a power source, an electrical power output to the water pump, control circuitry enabled to switch power from the power source to the output to the water pump, and switching power from the power source to the power output to the water pump, causing recirculation in the pipe loop, based on presence and value of signals received from the flow sensor and the temperature sensors.

In one embodiment of the method the control circuitry switches power to the water pump in response to a signal that the flow sensor senses positive flow, and a pre-set difference in temperature sensed between the two temperature sensors. Also in one embodiment the method further comprises a step for adjusting the preset difference in temperature by a mechanism coupled to the control circuitry. In another embodiment the method further comprises overriding the control circuitry by a manual input to switch power to the water pump. And in one embodiment the control circuitry comprises one or more timing mechanisms for improving reliability of operation.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is an architectural overview of a plumbed hot water system using a recirculation pump according to existing art.

FIG. 2 is an architectural overview of a plumbed hot water system using a hot water recirculation pump according to an embodiment of the present invention.

FIG. 3 is a process flow chart depicting steps for recirculation of hot water through a hot water loop according to an embodiment of the present invention.

FIG. 4 is a rear elevation view of the control unit of FIG. 2 according to an embodiment of the present invention.

FIG. 5 is a front elevation view of the control unit of FIG. 2.

FIG. 6 is a bottom view of the control unit of FIG. 2.

FIG. 7 is an electrical diagram depicting control circuitry within the modular control unit of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

In various embodiments described in enabling detail herein, the inventor provides a unique system for managing the distribution of hot water in a plumbed system. The present invention is described using the following examples, which may describe more than one relevant embodiment falling within the scope of the invention.

FIG. 1 is an architectural overview of a plumbed hot water system 100 using a recirculation pump 104 according to existing art. System 100 includes a hot water heater (HWH) 101 that may be gas or electrically heated (heating apparatus not illustrated). A cold water line 102 is plumbed into HWH 101 delivering water into the tank to be heated. A hot water line or loop 103 is plumbed from HWH 101 and distributes hot water to hot water draw points in system 100.

In this example, a hot water recirculation pump 104 is added to system 100 to constantly pull hot water through loop 103 and past draw points in the system. The draw points illustrated herein include a Tub/Shower unit 105, a Faucet/Sink unit 106, and a clothes washer unit 107. In one example, one or more switches and wiring (not illustrated) are present for controlling power to pump 104. In one example, a timer (not illustrated) may be included for automatic switch activation based on time of day, for example. The switches may be provided at draw points 105 through 107 or one switch at a central location to activate and run the recirculation pump.

In this example of existing art, pump 104 may be constantly on during an “active period” of hot water necessity that might be defined in a timer connected to the pump. In lieu of a timer, a manual switch or multiple switches may be activated from draw points or from a central location to start and stop pump 104 as described above. Either implementation is less than optimal from the standpoint of water and energy conservation. Loop 103 runs past draw points 105, 106, and 107, through pump 104 and into the incoming cold water line to HWH 101. In either implementation the hot water availability at draw points 105 through 107 is not well regulated.

FIG. 2 is an architectural overview of a plumbed hot water system using a hot water recirculation pump 204 according to an embodiment of the present invention. A hot water heater (HWH) 201 is provided having a cold water line 202 plumbed thereto for water inflow and a hot water loop or line 203 plumbed therefrom for hot water distribution to flow points 205 (Tub/Washer), 206 (Faucet/Sink), and 207 (Clothes Washer). HWH 201 may be electrically or gas heated or with a tank or tankless without departing from the spirit and scope of the present invention.

An electronic control apparatus 208 is provided to control the distribution of hot water from HWH 201. Control unit 208 may be located at a point that may be proximal to HWH 201 and recirculation pump 204 such as within the space of a utility closet housing the components, for example. In a preferred embodiment, recirculation pump 204 plugs into control unit 208 for power. In this embodiment, control unit 208 is adapted to turn on or turn off power to a female AC plug receptacle (not illustrated) on control unit 208 that recirculation pump 204 plugs into. In this example connections to control unit 208 are logically depicted. In a preferred embodiment, control system 208 plugs into a wall electrical outlet and the recirculation pump is plugged into the control unit. It should be noted herein that in one implementation, pump 204 may be plugged in elsewhere and a control line may be provided from the control unit to an on/off switch (not illustrated) on the pump. Similarly, sensors may communicate over separate communication lines or over a single line or cable without departing from the spirit and scope of the invention.

Control unit 208 in one implementation includes a micro-processing unit (MPU), a memory (MEM), a power supply (PS), and circuitry adapted for actuating the pump wiring specifically based on sensor input received at the control unit in real time over another connection, such as a computerized communications port such as Universal

Serial Bus (USB) port. In this embodiment a first temperature sensor (TS 1) 210 is provided and connected to the hot water output line (203) of HWH 201. TS 1 is adapted to measure the temperature of the water in pipe 203 where it egresses HWH 201. TS 1 210 is electrically wired to control unit 208 and may constantly or periodically report the current temperature of the hot water leaving the water heater.

In one embodiment, TS 1 210 is an active sensor that takes temperature readings periodically and reports those to control unit 208. In another embodiment, TS 1 210 is a passive sensor that may be accessed periodically by the control unit to access the current temperature reading at egress of the water heater. TS 1 210 may, in one implementation be installed within the water line or plumbing fixture connected at egress and has direct contact with the hot water. In another implementation, TS 1 210 is installed over or onto the pipe exiting the hot water heater and actually measures the temperature of the pipe. It is sufficient to say that TS 1 210 measures the temperature of the output of the hot water heater.

A second temperature sensor (TS 2) 209 is provided and connected to a portion of loop 203 just before cold water ingress line 202 junction where the re-circulated hot water may mix in with incoming cold water into the water heater. TS 2 209 may be identical in some embodiments to TS 1 212. TS 2 measures the temperature of returning hot water just before it junctions with cold water line 202. In the course of operation it is expected that the temperature at hot water egress from HWH 201 will be greater than the temperature of hot water ingress into cold water line 202, especially after recirculation pump 204 has been off for a period of time allowing the water in hot water loop 203 to cool down. The difference in temperature may, in one embodiment, be used to define a temperature range window that may be specified in an algorithm to determine whether recirculation pump 204 will be powered on or off.

A flow sensor (FL S) 211 is provided in this embodiment to sense a draw of hot water through hot water loop 203. Control unit 208 may continuously or periodically monitor flow sensor 211 to determine if there is a draw on hot water loop 203 via one or more hot water line draw points (205-206). In one implementation, the control system includes an Arduino Micro™ micro-controller, 2 Thermal Probe DS 18B20 sensor devices, a SEN-HZ43WB G3/4″ water flow sensor, a 15 amp relay, and a 5 volt power supply.

In one embodiment, SW 213 and or firmware (FW) may be provided in MEM on control unit 208 that provides instruction for the control unit to monitor flow sensor 211 for any draw events. SW 213 may be further adapted to read temperature measurements at or sent to control unit 208 by temperature sensors TS 1 and TS 2. SW 213 may determine, based on the temperature readings whether the temperature difference is larger than or falls within a preset temperature range. If there is a hot water draw event, as long as the temperature difference between the two sensors remains within a preset temperature range or window, the recirculation pump may remain in off mode. If there is a hot water draw event and the temperature difference between the two sensors (TS 1, TS 2) is larger than the threshold range then the recirculation pump may be powered on by control system 208 to begin circulating hot water through loop 203 and back to cold water ingress line 202. In this way, as long as there are hot water draw events, the water circulated through loop 203 is prevented from cooling beyond a certain temperature defined within the temperature range making user access to the hot water more efficient and economical. Hot water loop 203 may include more draw points or access points, such as points 205 through 207 without departing from the spirit and scope of the present invention. Hot water loop 203 may in one embodiment include more than one recirculation pump. Hot water loop 203 may also include more than two temperature sensors without departing from the spirit and scope of the invention. In one embodiment of the invention, control unit 208 may be adapted to control more than one recirculation pump on one or more than one hot water loop that may share HWH 201. In the case of two separate hot water loops, the loops may be isolated from one another by an electronically operated valve such as a ball valve (not illustrated). Such implementation may be useful in a commercial environment such as a multiple floor hotel with multiple rooms on each floor.

In one embodiment control system 208 may be adapted to accept user input from an authorized individual whereby such individual may program which of more than one hot water loops will be isolated from or shut off from the other hot water loop(s) in the plumbed system, and which one or ones of the loops will be active and recirculating hot water. In the example of a hotel, there may be one hot water loop at each floor level wherein if room occupation by patrons is controlled to specific floors, only the loops covering the occupied floor may be activated for hot water recirculation. In this way it is possible to conserve resources (water, energy) by only using recirculation on a single loop. It will also be apparent that there may be more than one water heater with a tank or tankless present in a plumbed system without departing from the spirit and scope of the present invention. The number of temperature sensors and flow sensors may vary without departing from the spirit and scope of the present invention.

FIG. 3 is a process flow chart 300 depicting steps for recirculation of hot water through a hot water loop according to an embodiment of the present invention. There is a delay period as a period of not immediately starting the pump when a draw is registered. By way of explanation assume the system has been off for quite some time, such that water in the hot water loop is cold. If someone draws hot water and then relatively quickly shuts the hot water off, that action may not draw enough hot water to the temperature sensor on the outlet side of the water heater to trigger a significant temperature difference, so the pump will not turn on. To account for this situation a delay period is triggered each time the control unit returns to monitoring the flow sensor. Then, with the sensing of a draw, the pump will turn on immediately only if the delay period has expired. In one embodiment a delay period of ten minutes is reasonable, but other periods may be set depending on the installation. This operation allows the temp sensor to heat up while the unit is checking for a temperature differential which it does for say 10 seconds after a draw event occurs. The delay period is continually reset every time the control unit returns to monitoring the flow sensor via steps 315 and 309 after hot water hot water is drawn, so this immediate turning on of the pump only happens after the there has been no hot water drawn for the length of the delay period.

Following the flow in FIG. 3, at step 301 the control unit is monitoring for draw (flow sensor) and the pump is off. At step 302 if there is no draw control loops back to step 301. If at step 302 a draw is recognized the controller checks at step 303 if the delay period has expired. If so, the pump is turned on at step 304. If not, the temperature at the temperature sensors is checked at step 305, which has a time period. In one embodiment ten seconds is reasonable. At step 306 the system determines the temperature difference between the two sensors. At step 307, if the difference is smaller than a preset threshold the system checks at step 308 to see if the temperature check period has expired. If the temperature check period has not expired control loops back through the temperature check step 305. If, however, the temperature check period has expired, the pump is turned off at step 316 if it was turned on in step 304, and the delay period timer is reset at step 309. Control reverts to step 301.

If at step 307 the temperature difference is larger than the preset threshold the pump is turned on (or left on as a result of step 304) at step 310. The system then rechecks temperatures at step 311, calculates difference at step 312. If the difference is above the threshold value at step 313 control loops back through step 311. If at step 313 the difference is less than or equal to the preset value the pump is turned off at step 314, and the delay timer is reset at step 315, returning control again to step 301.

In one aspect it is possible that there is no hot water, therefore the temperature at both sensors would be the same. In that case the recirculation pump may be kept off by default. If the water is heated by the water heater, then the temperature sensor at the water heater will be hotter than the temperature at the end of the recirculation loop prior to the junction where the returning hot water mixes with incoming cold water before entering the water heater provided there has been a draw on the hot water loop as measured by the flow sensor and identified as a hot water draw by the control unit. Therefore in periods of no draw the recirculation pump stays off. After initial draw, the system kicks in to manage hot water accessibility for the users.

FIG. 4 is a rear elevation view of control unit 208 of FIG. 2 according to an embodiment of the present invention. FIG. 5 is a front elevation view of unit 208. FIG. 6 is a bottom view of unit 208. Referring now to FIG. 4 Unit 208 may be of the form of a plug-in module. In this respect control unit 208 is modular and may be plugged into a wall outlet near the hot water heater via standard male AC power plug 401. Unit 208 may therefore reside within the local proximity of the hot water heater such as within a utility closet enclosing the tank. Unit 208 includes a multiple port 402 connecting input from the flow sensor and temperature sensors and providing power to the sensors.

Referring now to FIG. 5, opposite male AC power input plug 401 is a female AC power output plug 501 adapted to accept a male AC power plug from the recirculation pump. Module or unit 208 may be housed within a utility grade polymer housing. Referring now to FIG. 6, Port 402 is a multiple port connector serving +5 V, GND, flow sensor and temperature sensors. In one embodiment, unit 208 receives sensor data from the flow and temperature sensors via port 402. The recirculation pump may be plugged into female receptacle 501, while the unit itself is plugged into a standard wall outlet. It is noted herein that all of the control circuitry is housed within modular unit 208.

A switch 403 is provided that, when closed, places the unit into a setup mode. Setup mode is useful for installations wherein the unit does not reliably start the pump when a faucet is opened and closed, indicating that the sensitivity of the flow sensor needs to be increased, which may be done via adjusting a potentiometer. Switching into setup mode causes the pump to turn on for about ten seconds and then to turn off regardless of the temperature values. This way the sensitivity of the flow sensor can be set without having to unplug the unit to reset it and even if the loop is up to temperature. This adjustment may also be used if the unit turns on when a cold water faucet is closed abruptly as, for example, when a toilet finishes filling. Sometimes this is enough to send a pulse through the plumbing and trigger the flow sensor if it is too sensitive.

In an alternative embodiment circuitry shown in FIG. 7 may also include Bluetooth circuitry and code to allow updating logic for the controller and to adjust values for timer and temperature settings and the like via a computerized device such as a laptop computer or a smart telephone. In yet another variation WiFi circuitry and code may be included to allow updating logic for the controller and to adjust values for timer and temperature settings and the like via a computerized device such as a laptop computer or a smart telephone.

In some embodiments a manual on-off switch is included in the modular unit to over-ride the controller in the unit, so the recirculation pump may be powered on and off regardless of sensed conditions. Such a switch is depicted in FIGS. 4, 5 and 6 as element 403.

FIG. 7 is an electrical diagram depicting one possible arrangement of control circuitry 700 within modular unit 208 of FIG. 2. It will be apparent to the skilled person that there may be many alternatives to this circuitry, while still accomplishing the purposes. Logic for circuitry 700 in this particular example is based on a microprocessor 701 receiving input from flow sensor 211, temperature sensor (1) 210 and temperature sensor (2) 209. The microprocessor is powered by a 5 V DC power supply connected to input from wall plug 401, and controls an electronic switch 703 to switch the main line from wall plug 401 to output 501 which powers pump 204.

It will be apparent to one with skill in the art that the recirculation pump control system of the invention may be provided using some or all of the mentioned features and components without departing from the spirit and scope of the present invention. It will also be apparent to the skilled artisan that the embodiments described above are specific examples of a single broader invention that may have greater scope than any of the singular descriptions taught. There may be many alterations made in the descriptions without departing from the spirit and scope of the present invention.

It will also be apparent to the skilled person that the arrangement of elements and functionality for the invention is described in different embodiments in which each is exemplary of an implementation of the invention. These exemplary descriptions do not preclude other implementations and use cases not described in detail. The elements and functions may vary, as there are a variety of ways the hardware may be implemented and in which the software may be provided within the scope of the invention. The invention is limited only by the breadth of the claims below. 

1. A hot water recirculation control unit, comprising: a housing; a standard male electrical wall plug integrated into a first wall of the housing, the male wall plug connected to hot, neutral and ground electrical conductors in electrical circuitry within the housing; an electrically-operable power switch in the circuitry of the controller, connected on an input side to the hot electrical conductor; a standard female electrical wall plug integrated into a second wall of the housing, connected to neutral and ground and to the output terminal of the electrically-operable power switch; control circuitry including a processor, connected to the electrical conductors, the control circuitry having an output enabled to switch the electrically-operable power switch; and one or more input signal ports enabled to receive signals from two temperature sensors and at least one flow sensor, the signal ports connected to the control circuitry; wherein the control circuitry switches the electrically-operable power switch on or off, providing power to or disconnecting power from the standard female electrical wall plug, based on presence and value of signals received at the one or more input signal ports.
 2. The hot water recirculation control unit of claim 1 wherein the control circuitry switches the electrically-operable power switch on, providing power to the standard female electrical wall plug, in response to a signal that the flow sensor senses positive flow, and a pre-set difference in temperature is sensed between the two temperature sensors.
 3. The hot water recirculation control unit of claim 2 further comprising a mechanism enabling adjustment of the preset difference in temperature.
 4. The hot water recirculation control unit of claim 1 further comprising a manual input enabled to switch the electrically-operable power switch on and off.
 5. The hot water recirculation control unit of claim 2 wherein the control circuitry comprises one or more timing mechanisms for improving reliability of operation.
 6. A hot water recirculation system, comprising: a water heating source; a pipe loop from the water heating source supplying heated water to a plurality of draw points and returning to an input of the hot water heating source; a cold water supply line to the hot water heating source; a water pump in the pipe loop after the draw points and before the input to the water heating source; a flow sensor in the pipe loop to indicate positive flow of water, indicating a draw at one of the plurality of draw points; a first temperature sensor coupled to the pipe loop near the outlet of the water heating source; a second temperature sensor coupled to the pipe loop at a point after the plurality of draw points; and a controller having an electrical power input from a power source, an electrical power output to the water pump, and control circuitry enabled to switch power from the power source to the output to the water pump; wherein signals from the flow sensor and the first and second temperature sensors are coupled to the control circuitry and the control circuitry switches power from the power source to the power output to the water pump, based on presence and value of signals received from the flow sensor and the temperature sensors.
 7. The hot water recirculation system of claim 6 wherein the control circuitry switches power to the water pump in response to a signal that the flow sensor senses positive flow, and a pre-set difference in temperature sensed between the two temperature sensors.
 8. The hot water recirculation system of claim 7 further comprising a mechanism coupled to the control circuitry enabling adjustment of the preset difference in temperature.
 9. The hot water recirculation system of claim 6 further comprising a manual input to the control circuitry enabled to switch power to the water pump, overriding the control circuitry.
 10. The hot water recirculation system of claim 6 wherein the control circuitry comprises one or more timing mechanisms for improving reliability of operation.
 11. A hot water recirculation method, comprising: providing a pipe loop from a water heating source to a plurality of draw points and returning to an input of the hot water heating source; providing a cold water supply line to the water heating source; proving a water pump in the pipe loop after the draw points and before the input to the water heating source; sensing flow by a flow sensor in the pipe loop to indicate positive flow of water, indicating a draw at one of the plurality of draw points; sensing a first temperature by a first temperature sensor coupled to the pipe loop near the outlet of the water heating source; sensing a second temperature by a second temperature sensor coupled to the pipe loop at a point after the plurality of draw points; monitoring flow indication from the flow sensor and temperatures sensed by the temperature sensors at a controller having an electrical power input from a power source, an electrical power output to the water pump, and control circuitry enabled to switch power from the power source to the output to the water pump; and switching power from the power source to the power output to the water pump, causing recirculation in the pipe loop, based on presence and value of signals received from the flow sensor and the temperature sensors.
 12. The hot water recirculation method of claim 11 wherein the control circuitry switches power to the water pump in response to a signal that the flow sensor senses positive flow, and a pre-set difference in temperature sensed between the two temperature sensors.
 13. The hot water recirculation method of claim 12 further comprising a step for adjusting the preset difference in temperature by a mechanism coupled to the control circuitry.
 14. The hot water recirculation method of claim 11 further comprising overriding the control circuitry by a manual input to switch power to the water pump.
 15. The hot water recirculation method of claim 11 wherein the control circuitry comprises one or more timing mechanisms for improving reliability of operation. 